Generally, semiconductor devices include a plurality of circuits which form an integrated circuit fabricated on a semiconductor substrate. A complex network of signal paths will normally be routed to connect the circuit elements distributed on the surface of the substrate. Efficient routing of these signals across the device requires formation of multilevel or multilayered schemes, such as, for example, single or dual damascene wiring structures. The wiring structure typically includes copper, Cu, since Cu based interconnects provide higher speed signal transmission between large numbers of transistors on a complex semiconductor chip as compared with aluminum, Al, -based interconnects.
Within a typical interconnect structure, metal vias run perpendicular to the semiconductor substrate and metal lines run parallel to the semiconductor substrate. Further enhancement of the signal speed and reduction of signals in adjacent metal lines (known as “crosstalk”) are achieved in today's IC product chips by embedding the metal lines and metal vias (e.g., conductive features) in a dielectric material having a dielectric constant of less than 4.0.
In some interconnect structures, a diffusion barrier including TaN and Ta is employed. Such interconnect structures including a TaN/Ta diffusion barrier have good oxidation resistance properties. In yet other interconnect structures, a diffusion barrier that includes TaN and Ru has been proposed. One reason for using a diffusion barrier that includes TaN and Ru is that thin Cu seed layers (having a thickness of less than 300 Å) have better wettability on Ru than on Ta. Ru is compatible for thin Cu seed related applications, but not Ta. Thin Cu seed related applications are the trend for future technology and are closely related to technology extendibility. Also, Ru can be deposited through plasma vapor deposition (PVD), chemical vapor deposition (CVD) and atomic layer deposition (ALD), but Ta can only be deposited through PVD, which has a big technology extendibility concern on conformality. The use of a TaN/Ru diffusion barrier however is problematic since Ru as the outer diffusion barrier is not a good oxidation resistance barrier.
In view of the above, there is an ongoing need for providing an interconnect structure that includes a diffusion barrier structure in which Ru is used and the problem associated with Ru oxidation has been obviated.